The present invention relates to an intake device for a mixture-compressing internal-combustion engine and, more particularly, to the type of intake device which uses an electric heating element fitted in the intake channel downstream of an injection nozzle and comprises a sheet-like heating body essentially flowed around by the combustion air and a base part via which the heating body is held in an essentially heat-insulated manner on the cylinder head. The surface of the heating body facing the injection nozzle is impinged at least by part of the quantity of fuel discharged by the injection nozzle, and a connection for the heating body to a power source is provided in the base part.
An intake device is shown in DE-C 34 26 469 in which an annular heating element is provided close to the engine valve opening, into which element the fuel is injected obliquely. The heating ring lays with its longitudinal axis essentially in the direction of flow. It is disadvantageous in the case of such a heating ring that the fuel jet had to be introduced obliquely through one of the open end faces of the heating ring into the ring. Since the fuel jet fans out when it leaves the injection nozzle, the heating ring must either be arranged relatively close to the injection nozzle, or the fanning-out fuel jet to a great extent impinges on the closed annular end face of the hearing ring and its outer casing. As a result, an undesired swirling of the injected fuel jet occurs at the hearing ring element. The latter case occurs in particular whenever the heating ring is fitted in the desired way as close as possible to the engine valve opening and the injection nozzle can only be provided some distance away from the heating ring. Such distances are often inevitable due to installation conditions.
Moreover, an intake device which coincides in its construction substantially with that of the known intake device, and also has the disadvantage of the latter, is shown in EP-A 0 343 652.
It is an object of the present invention to provide an improvement in intake devices and, in particular, to avoid formation of fuel condensate which is harmful in exhaust emissions.
This object is achieved in accordance with the present invention by configuring the heating plate in a flat form which is held on a base part by a narrow support which is transverse to the direction of combustion air flow. The fuel-impinged surface of the plate runs parallel or at angle with respect to the longitudinal axis of the intake channel.
According to the present invention, the heating plate is impinged obliquely by the fuel jet directed at the engine valve opening. As a result, the heating element forms only an extremely low flow resistance and thus excessive uncontrolled swirling effects in the region of the hearing element are avoided.
In the case of one embodiment of the present invention in which the heating plate is integrated in the wall of the intake line, the flow resistance brought about by such a heating element is minimized to the greatest extent. Since the fuel jet is to have as little contact as possible with the walls of the intake line on its way into the valve opening, however, a heating element integrated into the intake line wall cannot be arranged in the main flow axis of the fuel jet. Rather, it is necessary in this embodiment to divide the fuel jet into a main jet and a secondary jet, with the secondary jet being substantially smaller with respect to its rate of flow than the main jet. The secondary jet is produced by an additional opening in the injection nozzle. The secondary jet is directed to impinge directly on the hearing element laying flush in the line wall and is reflected back from there into the main stream.
Although the present invention does produce a somewhat greater resistance due to the free arrangement within the inlet channel, it has the advantage that a good fuel heating with a simultaneous good air preheating can take place due to the heating element plate being flowed around on virtually all sides. Moreover, the heating plate protruding freely into the intake channel can be directed into the injection jet at an acute angle in such a way that a dividing of the injection jet into a main jet and a smaller secondary jet is unnecessary.